在Python中实现一个点类

Question

所以我试图实现一个点类，它创建一个点，然后旋转，缩放和转换点。这是我目前写的。

class Point: 
    ''' 
     Create a Point instance from x and y. 
    ''' 
    def __init__(self, x, y): 
     self.x = 0 
     self.y = 0 

    ''' 
     Rotate counterclockwise, by a radians, about the origin. 
    ''' 
    def rotate(self, a): 
     self.x0 = math.cos(this.a) * self.x - math.sin(this.a) * self.y 
     self.y0 = math.sin(this.a) * self.x + math.cos(this.a) * self.y 

    ''' 

     Scale point by factor f, about the origin. 
    Exceptions 
     Raise Error if f is not of type float. 
    ''' 
    def scale(self, f): 
     self.x0 = f * self.x 
     self.y0 = f * self.y 

    ''' 
     Translate point by delta_x and delta_y. 
    Exceptions 
     Raise Error if delta_x, delta_y are not of type float. 
    ''' 
    def translate(self, delta_x, delta_y): 
     self.x0 = self.x + delta_x 
     self.y0 = self.y + delta_y 

    ''' 
     Round and convert to int in string form. 
    ''' 
    def __str__(self): 
     return int(round(self.x)) 

此代码中的某些内容正在生成错误。现在我还没有实现错误捕捉和我有在顶部

class Error(Exception): 
    def __init__(self, message): 
     self.message = message 

错误的方法，但我将如何捕捉错误，如果某个变量是float类型呢？

这里的if语句我使用的一个：

def __init__(self, x, y): 
     if not isinstance(x, float): 
      raise Error ("Parameter \"x\" illegal.")   
      self.x = x 
      self.y = y 
     if not isinstance(y, float): 
      raise Error ("Parameter \"y\" illegal.") 
      self.x = x 
      self.y = y 

但是，这让我的缩进错误。那么，我怎样才能打印出一个错误信息，说明哪个变量导致了问题？

Answer 1

如果该变量不是浮点数，您将得到一个TypeError。你几乎可以像这样“捕捉”这些错误;

try: 
    pass # your stuff here. 
except e as TypeError: 
    print e # this means a type error has occurred, type is not correct. 

另外，这将是值得阅读的检查正确的类型在开始assert; https://wiki.python.org/moin/UsingAssertionsEffectively

Answer 2

如果你想提高一个例外，它做了点的初始化：

def __init__(self, x, y): 
    if not isinstance(x, float) or not isinstance(y, float): 
     raise Error("Point's coordinates must be floats.") 
    self.x = x 
    self.y = y 

或转换坐标浮动：

def __init__(self, x, y): 
    self.x = float(x) 
    self.y = float(y)